Many conventional power switches are designed for direct current applications and, thus, only block electric current that is flowing in one direction. Such power switches are often simply placed back-to-back to operate in an alternating current environment. Unfortunately, this results in a relatively high inductance in the overall system as the power and return lines are uncoupled. Because current sharing is not guaranteed to be equally distributed among the multiple power switches, the power switches are de-rated to ensure that the power switches stay within design limits, requiring more power switches than may otherwise be required. This in turn increases costs and system footprint.
In order to handle a particular amount of current, power switches often implement multiple parallel current paths through the switch. Components in such paths, such as, by way of non-limiting example, metal-oxide-semiconductor field-effect transistors (MOSFETs) and diodes, conduct greater amounts of current as they rise in temperature. It is common for such components to heat at a quicker rate than other components in the same switch because of their proximity to other heat-producing electronic components. For example, components located in a center portion of a switch may heat at a quicker rate than components located on an edge portion of the switch. As a component rises in temperature, it begins to conduct greater amounts of current, which leads to an increase in temperature. This cycle ultimately can lead to a thermal runaway of the component and to a failure of the switch.
Accordingly, there is a need for bi-directional switches that have low overall inductance and that force current sharing evenly among multiple parallel current paths through the switch.